Massachusetts is holding a special election to replace Ted Kennedy, who passed away in August 2009.
The primary was held in December 2009, with a general election to follow in January 2010.

Scott Brown won the Republican primary,
and Martha Coakley won the Democratic primary.
In addition, Joe L. Kennedy qualified by petition for the general election ballot, representing the Libertarian Party.

In the interim, Paul Kirk was appointed as a "placeholder" senator, pending the general election result.
The Democratic Massachusetts governor, Deval Patrick, appointed Kirk after the Massachusetts legislature changed the law about interim appointments, immediately following Sen. Kennedy's death.

The Democrat-dominated Massachusetts legislature was criticized for that action, since they had only a few years prior changed the law in the other direction, to bar interim senate appointments,
anticipating that John Kerry might win the presidential election,
and they were opposed to allowing then-Governor Mitt Romney, a Republican, to replace Kerry with a Republican appointee.

OnTheIssues.org excerpts:(click on issues for details)

Budget & EconomyScott Brown: People are angry over tax and spend mentality and $12T debt.
Martha Coakley: Economic system spiraling out of control; go after Wall St.
Stephen Pagliuca: Managing director at Bain Capital; trained as accountant.
Scott Brown: Let private enterprise try to get us out of this mess.
Scott Brown: No cap on bankers' salaries.

CorporationsStephen Pagliuca: Not right to pay bankers bonuses with 320,000 unemployed.

Government ReformMartha Coakley: Current FEC reporting on donors & meetings is enough.
Michael Capuano: If meetings are made public, people will not visit Senators.
Scott Brown: Let president decide on nominees.